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xvil                     CHARACTERS OF ANTHROPO1DEA                    555
the Catarrh!nes ttnd Platyrrhines. In the former the nostrils look
downward and are close together; in the latter they are separated
by a broad cartilaginous septum, and the apertures are directed
outwards. But numerous other points of difference separate these
two groups of the Monkey tribe. The Catarrhines often have
those remarkable ischial callosities., patches of hard skin brightly
coloured ; the tail may be totally wanting as a distinct organ, as
is the case, for instance, with the Anthropoid Apes ; there are
often cheek pouches, so that, as Mr. Lydekker has remarked, if a
Monkey be observed to stow nuts away in its cheeks for future
reference, we may be certain that its home is in the Old World,
for the Catarrhines are exclusively denizens of the Old World,
while the Platyrrhines are as exclusively 3sTew World in range.
Again, those of the Catarrhines which do possess a long tail,
such as the members of the genus Cercocebus, never show the
least sign of prehensility in that tail. The teeth of the Catar-
rhines are invariably thirty-two in number, the formula being
If C^Pinf Mž = 32. -
In the Old-World Apes there is a bony external auditory
meatus, which is wanting (as a bony structure) in the Platyr-
rhines. The late Mr. W. A. Forbes pointed out that in most of
the New-World forms the parietals and the malars come into
contact; in the Monkeys of the Old World they are hindered
from coming into contact by the frontals and the alisphenoids.
The Platyrrhines may have the same number of teeth; this is
the case with the Marmosets, but in them there are three pre-
molars arid two molars; iix the remaining New-World Monkeys
there are thirty-six teeth, but of these three are premolars and
three molars,
Not only are these two groups of the Primates absolutely
distinct at the present day, but they have been, so far as we
know, for a very long time, since no fossil remains of Monkeys
at all intermediate have been so far discovered. This has led tc
the suggestion that the Monkeys are what is termed diphyletic
i.e. that they have originated from two separate stocks o
ancestors. It is hard, however, to understand on this view tin
very great similarities which underlie the divergences that hav*
just been mentioned. But, on the other hand, it is equally har<
to understand how it is that, having been separated from eacl
other for so long a period, they have not diverged further ii